Process and catalyst for the selective production of α-alkylcinnamaldehyde

ABSTRACT

The selective obtainment of α-alkyl cinnamaldehydes, such as Jasmine aldehyde is carried out by a process that involves two consecutive reactions: acetalization of an n-alkyl aldehyde by direct reaction with an alcohol or by transacetalization followed by the reaction between said acetal and aromatic aldehyde such as benzaldehyde using molecular sieves with regular pore distribution in the range of micro and mesopores and between 6 and 100 Å as acid catalysts.

This is the U.S. National Stage Application of PCT/E598/00017 filed Jan.23, 1998.

INTRODUCTION

The present invention describes the preparation of α-alkylcinnamaldehydes and preferably, the preparation ofα-n-amylcinnamaldehyde (Jasmine aldehyde), through aldolic condensationcatalyzed by zeolite type solid acids.

α-n-amylcinnamadehyde is a substance with a violent scent and it iscommonly used in perfumery. The production of α-n-amylcinnamaldehyde canbe carried out through aldolic condensation between heptanal andbenzaldehyde using alkaline catalysts.

A difficulty with aldol condensation is that both reagents can undergoside reactions giving rise to by-products that reduce the yield of alkylcinnamaldehyde and that furthermore they can provide an unpleasantscent, thus reducing the quality of the perfume. One of these undesiredreactions is self-condensation of n-alkyl aldehyde, which can beinhibited to a great extent, by keeping the concentration of thisreagent relative to that of the benzaldehyde in the reaction mixturevery low. Therefore, this methodology requires long addition times ofheptanal, leading to the use of batch reactions with long reaction timesand renders impractical the use of plug-flow continuous reactors.

Further by-products that are formed in these conditions are thoseresulting from the limited stability of benzaldehyde which tends todisproportionate via the Cannizzaro reaction to yield Benzes alcohol andbenzoic acid, which in turn reacts with the alkaline catalyst, andtherefore, causing the neutralization of the catalyst.

BACKGROUND OF THE INVENTION

A. Weissenborn in East German patent 11,191 (1956) describes a producefor the preparation of Jasmine aldehyde wherein the catalysts are Ni, Coor Fe salts of carboxylic acids. The reaction is carried out at thetemperature range of 180-190° C., in the presence of toluene in order tofacilitate azeotropic distillation of the water and the heptanal isadded slowly to the reaction mixture. Yields around 80% of Jasminealdehyde are obtained.

R. Mahrwald and H. Schick in East German patent DD 287,712 (1991)describe a procedure wherein the aldolic condensation between heptanaland benzaldehyde is accomplished in the presence of Titanium compounds(tetraisopropiltitanium) and toluene as the azeotropic agent. Yieldsaround 56% of Jasmine aldehyde are obtained.

L. S. Payne in European patent 392,579 (1990) describes a procedure forthe selective preparation of α-cinnamaldehydes by aldolic condensationin two phases, using glycols (especially ethylene glycol) as solventsand sodium or potassium hydroxides as catalysts. Yields around 90% ofα-cinnamaldehyde are obtained.

P. Mastagli et al. in Bull. Soc. Chim. France, 1955, p. 268, describethe preparation of Jasmine aldehyde using anionic exchange resins(IR-4B) as catalysts. The yields obtained varied between 2 and 12%.

The same author describes in Compt. Rend. 1957 vol. 244, p. 207, aprocess starting from n-alkyl aldehyde and benzaldehyde acetals using asa catalyst a mixture of an acid catalyst (cationic exchange resin) and abasic catalyst (anionic exchange resin) in order to produce thehydrolysis and aldolic condensation respectively. The yields obtainedvaried between 5 and 28%.

A. Sakar et al. in Ind. J. Chem., 1986, vol. 25,p. 656 accomplishaldolic condensation using potassium carbonate and a phase transfercatalyst such as benzyltriethylammonium chloride. On the other hand, D.Abenhaim et al in Synthetic Comm., 1994, vol. 24, p. 1199 carry outcondensation using the same type of catalysts but under microwaveeffect. In both cases yields around 80% of Jasmine aldehyde areobtained.

BRIEF DESCRIPTION OF THE INVENTION

This invention describes the selective obtainment of α-alkylcinnamaldehydes and specifically, Jasmine aldehyde, by direct reactionbetween the acetal of n-alkyl aldehyde (heptanal) and benzaldehyde wherezeolites and zeotypes with medium and large pore diameters with 10 andpreferably 12 member rings, as well as mesoporous molecular sieves areused as acid catalysts.

The process involves a first acetalization step which is carried outdirectly with an alcohol or through transacetalization using trialkylorthoformate (TOF) in the presence of the above-mentioned catalysts. Thesecond step involves the elimination of the remaining alcohol or TOF bydistillation and addition of benzaldehyde.

These acid catalysts subsequently cause slow hydrolysis of the acetaland mixed aldolic condensation, maintaining at all times a lowconcentration of the n-alkylaldhyde with respect to the benzaldehyde,thus obtaining the α-alkyl cinnamaldehydes with high yields andselectivities.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates the use of acid zeolites and mesoporousmolecular sieves, that in a certain way could be assimilated to zeotypematerials, as selective catalysts in the aldolic condensation betweenacetalizated n-alkyl aldehydes and benzaldehyde and in order to obtainα-alkyl cinnamaldehydes with yields higher than 80%.

The first stage of the process involves the acetalization of thealdehyde which takes place according to conventional procedures in acontinuous or discontinuous batch reactor or in a continuous fixed orfluidized bed reactor filled with the catalyst. The reaction temperatureranges from 25 to 280° C. When the transacetalization method is used,the aldehyde and the corresponding trialkyl orthoformate molar ratio arebetween 1:1 and 1:10 preferably between 1:2 and 1:5.

Short chain saturated primary alcohols and glycols are the preferredalcohols. Methanol, ethanol, propanol and ethylene glycol arenon-restrictive examples.

The second step of the reaction, and after distillation of the remainingalcohol or TOF, involves the addition of benzaldehyde to the reactionmixture. The heptanal/benzaldehyde molar ratio are between 1:1 and 1:10m preferably between 1:2 and 1:5.

The reaction can be accomplished under inert atmosphere, such asnitrogen, and at a temperature ranging from 25 to 200° C., preferablybetween 50 and 150° C.

The amount of catalyst used is between 2 and 30% based on the weight ofthe n-alkyl aldehyde.

When the reaction is carried out in a batch reactor, at the end of thereaction the zeolite is filtered, washed with dichloromethane and thesolvent is evaporated.

The catalysts used in the present invention are zeolites and zeotypesspecifically of medium and large pore, preferably with 12 membered ringsand mesoporous molecular sieves since the geometric constraints, due tothe poor size, make it possible to obtain products with highselectivities from mixed aldolic condensation.

The zeolite catalysts that meet the previous specifications are, amongothers, the following (the initials between brackets being accepted bythe International Zeolite Associations (see W. M. Meier and D. H. Olsonin Atlas of Zeolites Structure Types, 1992)

Mordenite (MOR), Ofretite (OFF), Omega (MAZ), Beta (BEA), Y (FAU),SSZ-24 (AFI), ZSM-12 (AFI) and SSZ-42

New zeolites which combine channels of 10 MR with 12 MR (MCM-22),SSZ-26, SSZ-36, CIT-1 and zeotypes with extra large pore sizes (20-100Å) such as M41S (such as MCM-41, (Beck et al. JACS, 114, 10834, (1992)),and amorphous mesoporous silica-alumina (SAM), with pore size in anarrow pore range (Bellussi et al.) Stud. Surf. Sci. 84, 93 (1994)) arealso applicable.

The catalysts, prior to be used, have to be prepared in their acid form.

Preparation of the Acid Form

The preparation of the acid form is accomplished directly by exchangewith an acid mineral when this is allowed by the zeolite stability, orif this is not possible, by an indirect method which consists in anexchange of its alkaline and alkaline earth cations by NH₄ ⁺ through atreatment with aqueous solution of ammonium chloride followed bycalcination, following conventional methods. It can also be prepared byexchange with di- or trivalent ions, followed by thermal treatment attemperatures between 100 and 600° C. for time intervals between 30minutes and 6 hours.

On the other hand, the number of acid sites, the distribution of acidstrength and the hydrophilic-hydrophobic characteristics of the catalystcan be controlled by varying its Si/Al ratio of the crystallineframework. The Al content of a zeolite can be modified directly duringsynthesis and this is not possible post-synthesis dealuminations arecarried out. They mainly consist of the extraction of aluminum from theframework by acid treatment or using a complexing agent such as EDTA.Furthermore, if desired, it is possible to introduce silicon at the sametime by chemical treatment with reagents such as (NH₄)2F₆ Si or SiCl₄.

EXAMPLES Example 1

Acetalization of heptanal and subsequent condensation with benzaldehydein the presence of zeolitic catalysts with a different structure.

Immediately before its use, the catalyst, in an amount equivalent to 10%(1.1 g) of the weight of the heptanal, is activated by heating at 100°C., under pressure of (1 mm Hg) for 2 h. After this time, the system isallowed to cool at room temperature and 11.5 g (0.1 mol) of heptanaldissolved in 150 ml. of methanol are added. The solution is heated atthe reflux temperature of methanol during the time necessary to achievean acetal (1,1-dimethoxyheptane) yield of around 90%. Thereafter, themethanol is evaporated and 10.6 g (0.1 mol) of benzaldehyde) are added.The condensation reaction is carried out under magnetic agitation at125° C., under a nitrogen atmosphere for a reaction time between 4 and16 h. After this time the catalyst is filtered and washed repeatedlywith dichloromethane. The crude of the reaction is analyzed by gaschromatography-mass spectrometry. The Jasmine aldehyde yield in molar %,for the different catalysts, is:

    ______________________________________                                        Catalyst   Jasmine Aldehyde Yield (%)                                         ______________________________________                                        MCM-41     87                                                                   SAM 83                                                                        HY 75                                                                       ______________________________________                                    

Example 2

Acetalization and condensation between benzaldehyde and1,1-dimethoxyheptane in the presence of MCM-41 catalyst with differentbenzaldehyde/heptanal molar ratios.

In the same conditions as in Example 1, the reaction is carried out inthe presence of MCM-41 catalyst with a Si/Al ratio of 14, and usingdifferent benzaldehyde/heptanal molar ratios (1:1, 1:3 and 1:5). Theresults show that the variation of the ratio of reagents has littleinfluence on the selectivity to jasmine aldehyde, obtaining final yieldsin the neighborhood of 85%.

Example 3

Influence of the temperature on the condensation reaction in thepresence of MCM-41.

In the same conditions as in Examples 1 and 2, the reaction is carriedout in the presence of MCM-41 catalyst with a Si/Al ratio of 14 atdifferent reaction temperatures. The Jasmine aldehyde yield obtainedafter one hour reaction time is shown on the table:

    ______________________________________                                        Temperature (° C.)                                                                   Jasmine Aldehyde Yield (%)                                      ______________________________________                                        100           10                                                                125 60                                                                        140 70                                                                      ______________________________________                                    

What is claimed is:
 1. A process for the preparation of α-alkylcinnamaldehydes, the process comprising a first step of acetalization ofan n-alkyl aldehyde by direct reaction of the aldehyde with an alcoholor transacetalization with trialkyl orthoformate for obtainingn-alkyladehyde acetal, and a second step wherein the acetal andbenzaldehyde or a substituted benzaldehyde, are subjected tocondensation using an acid catalyst in the absence of a basic catalyst,wherein the acid catalyst is an acid form of a molecular sieve having apore distribution of 6 to 100 Å selected from the group consisting ofmesoporous molecular sieves, microporous molecular sieves and molecularsieves having micropores and mesopores.
 2. A process according to claim1 wherein the molecula sieve is a zeolite selected from the groupconsisting of Beta, Y, Mordenite, Omega, MFI, SSZ-24, SSZ-26, SSZ-33,CIT-1, SSZ-42, MCM-22 zeolites and isomorphic substitutions thereof withtrivalent ions selected from Al, B, Ga, Fe.
 3. A process according toclaim 2 wherein the zeolite has a framework Si/T'" ratio in a range of 6and 400 wherein T'" refers to trivalent elements.
 4. A process accordingto claim 1 wherein the molecular sieve is a microporous silica-aluminumphosphate selected from the group consisting of SAPO-5, ALPO-8 and VPI-5and SAPO-37.
 5. A process according to claim 1 wherein the molecularsieve is a mesoporous material.
 6. A process according to claim 1wherein the condensation is carried out at a temperature between 25 and200° C. and a reaction time of between 10 minutes and 24 hours.
 7. Aprocess according to claim 1 wherein the alcohol used in theacetalization is selected from the group consisting of methanol,ethanol, propanol, ethylene glycol and propylene glycol.
 8. A processaccording to claim 1, wherein the n-alkyl aldehyde acetal is a RCHOacetal, wherein R is a linear or branched, saturated or unsaturatedchain having between 2 and 20 carbon atoms.
 9. A process according toclaim 5, wherein the mesoporous material is selected from the groupconsisting of M41S and SAM.
 10. A process according to claim 6, whereinthe reaction time is between 10 minutes and 5 hours, and the molar ratiobetween benzaldehyde and n-alkylaldehyde is from 1:1 to 1:10.
 11. Aprocess according to claim 6, wherein the reaction time is between 10minutes and 5 hours, and the molar ratio between benzaldehyde andn-alkylaldehyde is between 1:1 and 1:5.
 12. A process according to claim3, wherein the framework Si/T'" ratio is between 10 and 200.